This invention relates to a fuel delivery control apparatus for use with a multi-cylinder type internal combustion engine and, more particularly, to a fuel delivery control apparatus for terminating fuel delivery to some of the cylinders of the engine to avoid overspeed at high engine speeds.
Generally, it is the current practice to avoid engine overspeed by terminating fuel delivery to the engine operating at high speeds. For example, Japanese Patent Kokai No. 81-55323 discloses a fuel delivery control apparatus for operating an engine in a fuelcut mode to terminate fuel delivery to a a preselected cylinder group when the engine speed exceeds a predetermined value.
A disadvantage with such a conventional fuel delivery control apparatus is that the life of the engine is limited because of mechanical stresses caused by the temperature differences between the preselected cylinder group and the other cylinder group in the fuelcut mode of operation of the engine. In addition, the components associated with the preselected cylinder group will wear in a relatively shorter time than the components associated with the other cylinder group. Since the fuel delivery to the preselected cylinder group is terminated frequently, the combustion of the air-fuel mixture becomes unstable in the preselected cylinder group, resulting in emission of unburned fuel components therefrom. On the other hand, the other cylinders discharge hot exhaust gases which are mixed with the unburned fuel components discharged from the preselected cylinders to increase the exhaust gas temperature to a great extent causing a breakdown of the catalytic converter located in the exhaust passage of the engine when the fuelcut mode continues for a long period of time.